Seasonal analysis of cloud characteristics and radiative effect over the Iberian Peninsula using MODIS-CERES observations

We studied the seasonal evolution of clouds in four climatic regions within the Iberian Peninsula during the 2000-2012 period by using satellite data from CERES and MODIS instruments. We analysed cloud cover, cloud optical thickness, cloud-top temperature, and long- and shortwave radiative effect on top of the atmosphere for these four climatic regions. Cloud cover is larger in the north (regions 1 and 4) than in the south (regions 2 and 3) and shows a seasonal behaviour with summer minima for all regions. The maximum cover is found in region 1, with a mean yearly value of 61%. Region 3 shows the minimum cloud cover with an annual average around 43%. Cloud optical thickness ranges between 10 and 22 for low clouds, and between 8 and 20 for high clouds. Moreover, cloud-top temperature for low clouds is 265-285 K and in the range of 240-269 K for high clouds. Shortwave radiative effect is negative and ranging between −50 and −150 Wm⁻²for low clouds and from −50 to −175 Wm⁻²for high clouds. Longwave radiative effect is positive and in the range of 5-20 Wm⁻² for low clouds and around 75 Wm⁻² for high clouds. Generally, the longwave effect is lower than that for shortwave resulting in a net radiative effect of between 40 Wm⁻² and −150 Wm⁻² for low clouds and in the range of 10 - 90 Wm⁻² for high clouds.